No one that I know of has ever made the past "free" books available in any format outside of FCBD.

Occasionally you will get part of those free issues in a trade at a later date, but not in the same format as they are offered for the event.

My local shop was having a costume contest to win the free HC from Archaia for Mouse Guard. He ended up giving out 15 of those with plenty of others wishing they had gotten one too.

Many stores will end up getting some extra stock of some titles a week or two later, but most will charge for them to try and make back some of the expense they had to pay to get the books in the first place for the event.